Semiconductor devices are commonly found in modern electronic products. Semiconductor devices vary in the number and density of electrical components. Discrete semiconductor devices generally contain one type of electrical component, e.g., light emitting diode (LED), small signal transistor, resistor, capacitor, inductor, and power metal oxide semiconductor field effect transistor (MOSFET). Integrated semiconductor devices typically contain hundreds to millions of electrical components. Examples of integrated semiconductor devices include microcontrollers, microprocessors, charged-coupled devices (CCDs), solar cells, and digital micro-mirror devices (DMDs).
Semiconductor devices perform a wide range of functions such as signal processing, high-speed calculations, transmitting and receiving electromagnetic signals, controlling electronic devices, transforming sunlight to electricity, and creating visual projections for television displays. Semiconductor devices are found in the fields of entertainment, communications, power conversion, networks, computers, and consumer products. Semiconductor devices are also found in military applications, aviation, automotive, industrial controllers, and office equipment.
Semiconductor devices exploit the electrical properties of semiconductor materials. The atomic structure of semiconductor material allows its electrical conductivity to be manipulated by the application of an electric field or base current or through the process of doping. Doping introduces impurities into the semiconductor material to manipulate and control the conductivity of the semiconductor device.
A semiconductor device contains active and passive electrical structures. Active structures, including bipolar and field effect transistors, control the flow of electrical current. By varying levels of doping and application of an electric field or base current, the transistor either promotes or restricts the flow of electrical current. Passive structures, including resistors, capacitors, and inductors, create a relationship between voltage and current necessary to perform a variety of electrical functions. The passive and active structures are electrically connected to form circuits, which enable the semiconductor device to perform high-speed calculations and other useful functions.
Semiconductor devices are generally manufactured using two complex manufacturing processes, i.e., front-end manufacturing, and back-end manufacturing, each involving potentially hundreds of steps. Front-end manufacturing involves the formation of a plurality of die on the surface of a semiconductor wafer. Each die is typically identical and contains circuits formed by electrically connecting active and passive components. Back-end manufacturing involves singulating individual die from the finished wafer and packaging the die to provide structural support and environmental isolation.
One goal of semiconductor manufacturing is to produce smaller semiconductor devices. Smaller devices typically consume less power, have higher performance, and can be produced more efficiently. In addition, smaller semiconductor devices have a smaller footprint, which is desirable for smaller end products. A smaller die size may be achieved by improvements in the front-end process resulting in die with smaller, higher density active and passive components. Back-end processes may result in semiconductor device packages with a smaller footprint by improvements in electrical interconnection and packaging materials.
FIG. 1 shows a conventional package-on-package (PoP) Fo-WLCSP 10 with semiconductor die 12 stacked over semiconductor die 14 and enclosed by encapsulant 16. A build-up interconnect structure 18 is formed over the stacked semiconductor die 12-14 and encapsulant 16. Semiconductor die 12 and 14 are electrically connected to interconnect structure 18 with bond wires 20 and 22. Semiconductor die 24 is enclosed by encapsulant 26. A build-up interconnect structure 28 is formed over semiconductor die 24 and encapsulant 26. Semiconductor die 24 is electrically connected to interconnect structure 28 with bond wires 30. The build-up interconnect structure 18 is electrically connected to build-up interconnect structure 28 using bumps 32 formed around a perimeter of semiconductor die 24 and encapsulant 26.
The interconnect capability of Fo-WLCSP 10 is limited by the height requirement of encapsulant 26 formed around semiconductor die 24. That is, bumps 32 must be formed with sufficient size to span the gap between build-up interconnect structures 18 and 28. The gap is dictated by the height of encapsulant 26. Accordingly, the height of encapsulant 26 restricts the bump arrangement options, bump pitch, bump size, and input/output (I/O) count.